scalable for various applications WIRELESS COMMUNICATIONS Radiocommunications testers

Transcription

1 All-in-one tester for WiMAX mobile Mobile WiMAX in accordance with the IEEE e-2005 standard the first wireless communications system based on orthogonal frequency division multiplex (OFDM) for wireless broadband access in DSL quality is about to be implemented. As the first real all-in-one solution for cost-effective mass production of WiMAX mobile stations, the R&S CMW270 WiMAX communication tester is being introduced at exactly the right moment. scalable for various applications cial products are about to be launched. Rohde&Schwarz has actively supported WiMAX technology by offering dedicated tion platform [3]. Now, the company s R&S CMW270 WiMAX communication tester (FIG 1) is being introduced at exactly cost-effective mass production of mobile stations. ing of WiMAX mobile stations in production: test signal generation, test signal analysis and base station emulation. The new R&S CMW270 WiMAX communication tester from all these functions in a single box. The R&S CMW270 is specially designed for testing WiMAX mobile stations based on the IEEE e-2005 standard. It offers fast measurement functions for evaluating WiMAX signals, e.g. burst power, error vector magnitude (EVM), center frequency error and tor allows you to check the functionality of WiMAX mobile 22

2 station production FIG 1 All-inone solution for WiMAX mobile station production: The R&S CMW270 offers high-quality, highspeed measurement engineering plus the emulation of a base station. NEWS 196/ 08 23

3 stations under realistic WiMAX network conditions. Its integrated general-purpose RF generator and RF power meter make it ideal for a variety of measurement tasks. Owing to the tester s two bidirectional RF connectors and a high-power output, WiMAX mobile stations can directly be connected. External RF combiners or RF relays are not required. This means you do not need extra equipment for common applications which reduces costs for test setup while simultaneously increasing accuracy and reliability. Since the R&S CMW270 has a modular platform concept, it requirements in production, service and quality assurance. Moreover, hardware and software options, e.g. for WiMAX and a USB 2.0 interface allow remote control of the tester via an external PC. Operation via the conventional IEEE/IEC bus interface is also possible. The R&S CMW270 can also be remote-controlled within a LAN using the Windows XP Remote Desktop application. calibration functions for WiMAX chipsets An important step in the production of WiMAX mobile stations is the alignment of RF components such as RF trans- variations in frequency and level characteristics both in the transmit and receive path. To help ensure that the met during later operation, variations must be eliminated by alignment procedures during production. This includes mea- ues and storing the values in the mobile station. All this is usually done in the non-signaling mode. The DUT is run in a test commands. Many single measurements with different DUT and measuring instrument settings have to be performed this task, a test sequencer, which controls the calibration process, is used (FIG 4). FIG 3 Typical test sequence for WiMAX mobile stations in non-signaling mode. Test sequence Start I/Q offset calibration FIG 2 Measuring a WiMAX UL subframe: The R&S CMW270 provides fast measurement functions. Alignment of transmitter power Alignment of transmit frequency Calibration Alignment of receive power Alignment of receive frequency Transmitter measurements Receiver measurements 24

4 In close cooperation with the leading WiMAX chipset man- chipsets were carried out with chipset reference designs serving as a basis and using the R&S CMW270 as a measuring instrument. This joint effort yielded time-optimized function libraries for a variety of chipsets, and the libraries can be easily integrated into the end user s production test software. tests under realistic conditions (PHY) and the protocol functions in the medium access control (MAC) layer of the mobile station have to be tested under realistic conditions. This test is carried out by means of the R&S CMW270 which emulates a WiMAX base station using realtime signaling. This simulation is initiated with the network entry process, during which the mobile station is checked for correct synchronization and frequency correction. After the network entry process has been completed successfully, a functional test with various test scenarios can be performed via WiMAX signaling (FIG 5). The most important parameters that can be set are as follows: J Preamble code J MAC address J Number of DL symbols J OFDMA frame settings J Modulation type and coding rate Calibration test setup CMW270 FIG 4 Basic design of an automated calibration test setup. A test sequencer controls the calibration process. RF 1 OUT RF 1 COM RF RX 1 RX 0 / TX Chipset (DUT) LAN / IEEE LAN / USB PC with automatic test software FIG 5 User interface for WiMAX signaling. NEWS 196/ 08 25

5 WiMAX network entry process Start Scan for downlink channel Synchronization failed Cell rejection Cell rejection Synchronize with downlink Obtain UL and DL parameters Start initial ranging UL parameter adjustments Negotiate basic capabilities (SBC_REQ / SBC_RSP) The message logger records the following data: J Time stamp with 1 ms resolution J Link direction (UL/DL) J MAC management type (e.g. DL map, UL map, DCD, UCD) J J Status (success, continue) J Number of bytes J Offset frequency adjust J Power level adjust Signaling errors of the WiMAX mobile station can thus be recognized quickly and easily as they can be reproduced. Laten- the connection set up. This is due to time stamps and the display of repeated messages. FIG 6 Cell rejection Register with base station (REG_REG / REG_RSP) Establish IP connectivity DHCP & time of day Dynamic service establishment Normal operation Message flow during network entry process. SS authorization (optional) Key exchange Self test monitors hardware Fully tailored to the requirements in production, the R&S CMW270 WiMAX communication tester offers a builtin self-test (BIST) to monitor the internal hardware. The BIST functions are menu-controlled and allow you to perform diagnostics on the RF generator and RF analyzer. Plus, the internal bus systems of the tester as well as the plug-in modules are checked for correct function. The BIST functions can be remote-controlled and integrated into the test program. When applied regularly and combined with the statistical evaluation of results, these BIST functions will detect any deviation from the R&S CMW270 basic functions at an early stage an important preventive measure in avoiding the costs caused by a loss of production as a result of long downtimes. Well-prepared for future WiMAX requirements Message logger During the network entry process as well as during RF veri- place in the physical layer and in the MAC layer of a WiMAX mobile station (FIG 6). Errors may occur, for example, during the ranging process or a connection may drop completely. The R&S CMW270 message logger (FIG 7) records all messages between the WiMAX mobile station and the tester emulating a base station. The R&S CMW270 is also fully ready to meet future WiMAX standard expansions. Owing to its continuous frequency range from 70 MHz to 6 GHz, the R&S CMW270 already MHz for the analyzer and 70 MHz for the generator, the R&S CMW270 has enough margin to handle adjacent-channel measurements, for example. Plus, the tester is ready to accommodate a second measurement channel for testing MIMO applications. 26

6 Summary tion for WiMAX mobile station production: a high-quality, high-speed tester together with the emulation of a WiMAX base station in a single box and a shared user interface. It ware architecture makes it ideal for the production environment. Plus, the R&S CMW270 WiMAX communication tester is well prepared to handle future WiMAX developments such the MIMO multiple antenna technology. Erwin Böhler; Christian Hof Abbreviations DCD Downlink channel descriptor DSL Digital subscriber line DUT Device under test EVM Error vector magnitude MIMO Multiple input multiple output OFDM Orthogonal frequency division multiplex PER Paket error rate UCD Uplink channel descriptor WiMAX Worldwide interoperability for microwave access References [1] R&S TS8970 WiMAX Radio Conformance Test System State-of-the-art: all WiMAX RF certification tests. News from Rohde&Schwarz (2007) No. 194, pp [2] R&S SMx Signal Generators / R&S FSQ / R&S FSL Analyzers: WiMAX goes mobile new T&M solutions are required. News from Rohde&Schwarz (2006) No. 190, pp [3] R&S TS8970 WiMAX Radio Conformance Test System: Benchmark for the certification of WiMAX end products. News from Rohde&Schwarz (2006) No. 191, pp FIG 7 The message logger clearly displays the message flow of a WiMAX connection and allows convenient analysis. NEWS 196/ 08 27